Php 为什么左连接会产生不同的结果

在上运行查询时，此查询有什么问题 它将显示我想要的结果，但当在PHP页面上运行时，它将给出不同的结果

但当我在PHP页面上获取结果时，它也会给出空记录

如果没有这些空的子类别ID和子类别名称，如何获取记录

下面是PHP代码

    <table id="subCat1Table" class="table table-striped table-bordered" cellspacing="0" width="100%">
  <thead>
    <tr>
      <th>Sub Category ID</th>
      <th>Sub Category Name</th>
      <th>Root Category ID</th>
      <th>Root Category Name</th>
    </tr>
  </thead>
  <!-- <tfoot>
  <tr>
    <th>Sub Category ID</th>
    <th>Sub Category Name</th>
    <th>Root Category ID</th>
    <th>Root Category Name</th>
  </tr>
  </tfoot> -->
  <tbody>
    <?php
    $query1 = mysqli_query($conn, 'SELECT * FROM sub_category1 LEFT JOIN main_category ON sub_category1.main_category_id = main_category.category_id ');

    while ($row = mysqli_fetch_array($query1, MYSQLI_ASSOC))
    {
    // Result Assigning to Array
    $rows[] = $row;
    }
    // traversing Array
    echo("<pre>");
    print_r($rows);
    echo("</pre>");
    foreach($rows as $row):
    // Getting Values
    $subCategory1ID = stripslashes($row['sub_category1_id']);
    $subCategory1Name = stripslashes($row['sub_category1_name']);
    $rootCategoryID = stripslashes($row['category_id']);
    $rootCategoryName = stripslashes($row['category_name']);
    ?>
    <tr>
      <td><?php echo "$subCategory1ID"; ?> </td>
      <td><?php echo "$subCategory1Name"; ?> </td>
      <td><?php echo "$rootCategoryID"; ?> </td>
      <td><?php echo "$rootCategoryName"; ?> </td>
    </tr>
    <?php
    endforeach; //End ForEach loop
    ?>

  </tbody>
</table>

子类别ID
子类别名称
根类别ID
根类别名称

LEFT JOIN关键字返回左表（表1）中的所有记录，以及右表（表2）中匹配的记录。如果没有匹配项，则结果从右侧为NULL

---

您应该使用内部联接仅获取匹配记录

此处出现的问题是由于在while循环中为数组赋值

<?php
     $query = mysqli_query($conn, "SELECT * FROM sub_category1 INNER JOIN main_category ON sub_category1.main_category_id = main_category.category_id");

     while ($row = mysqli_fetch_array($query, MYSQLI_ASSOC)):
    // Getting Values
    $subCategory1ID = stripslashes($row['sub_category1_id']);
     $subCategory1Name = stripslashes($row['sub_category1_name']);
     $mainCatID= stripslashes($row['main_category_id']);
     $rootCategoryID = stripslashes($row['category_id']);
     $rootCategoryName = stripslashes($row['category_name']);
     ?>
     <tr>
       <td><?php echo "$subCategory1ID"; ?> </td>
                                <td><?php echo "$subCategory1Name"; ?> </td>
       <td><?php echo "$mainCatID"; ?> </td>
       <td><?php echo "$rootCategoryID"; ?> </td>
                                <td><?php echo "$rootCategoryName"; ?> </td>
     </tr>
    <?php
     endwhile; //End ForEach loop
?>

现在不分配给数组

您确定查询是相同的吗？它们是否在同一数据库上运行？发布数据集并添加代码高亮显示。

SELECT*

通常是一个糟糕的编码想法。为什么在不需要左连接时，首先要使用左连接呢？我认为，您生成的网格不正确。你能发布整个php代码吗？将

左连接更改为
连接，然后我们就可以回家了。
<?php
     $query = mysqli_query($conn, "SELECT * FROM sub_category1 INNER JOIN main_category ON sub_category1.main_category_id = main_category.category_id");

     while ($row = mysqli_fetch_array($query, MYSQLI_ASSOC)):
    // Getting Values
    $subCategory1ID = stripslashes($row['sub_category1_id']);
     $subCategory1Name = stripslashes($row['sub_category1_name']);
     $mainCatID= stripslashes($row['main_category_id']);
     $rootCategoryID = stripslashes($row['category_id']);
     $rootCategoryName = stripslashes($row['category_name']);
     ?>
     <tr>
       <td><?php echo "$subCategory1ID"; ?> </td>
                                <td><?php echo "$subCategory1Name"; ?> </td>
       <td><?php echo "$mainCatID"; ?> </td>
       <td><?php echo "$rootCategoryID"; ?> </td>
                                <td><?php echo "$rootCategoryName"; ?> </td>
     </tr>
    <?php
     endwhile; //End ForEach loop
?>